Not the only sort of spectacles on the beach (6)
I believe the answer is:
pebble
'beach' is the definition.
The answer and definition can be both natural objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for pebble that I've seen before include "Stone on beach" , "one of many on beach" , "Small fragment of rock" , "There are many on a stony beach" , "Small, round stone" .)